The need to change the down hole assembly of a drill string by actions carried out at the earth surface, to selectively drill a straight or directional hole, has long been recognized. The conventional practice of round-tripping the drill string to change the bottom hole assembly is costly in rig time and wear and tear on all machinery involved. The round-tripping is still a common practice although some progress has been made with development of alternate procedures and those known will be described.
The earliest known practice involved the use of a bendable sub used just above a drilling motor and held straight for straight hole drilling by a spear dropped down the drill string bore. The spear could be recovered by a wire line down the drill string bore and, in it's absence, a hydraulic cylinder responsive to drilling fluid flow would cause a knuckle joint in the bendable sub to deflect the centerline of the drilling motor. That sub was usable only above a drilling motor and long powerful drilling motors were hard to effectively deflect from a point so far above the drill head. Such apparatus would not work on the motor output shaft.
U.S. Pat. No. 4,319,649, issued Mar. 16, 1982, disclosed an eccentric stabilizer to be attached, preferably, at the lower end of a drilling motor housing. The stabilizer was capable of about 180 degrees of rotation relative to the motor housing. When the drill string was rotated to the right, for drilling, the stabilizer was concentric with the motor centerline. When the drill string was rotated to the left, the stabilizer would rotate to be eccentric. With drilling fluid flowing, the stabilizer would be locked eccentric and could be oriented by the drill string for controlled deflection of the proceeding hole. By stopping fluid flow and again rotating the drill string to the right, the stabilizer would again become concentric and straight hole drilling could proceed.
A drilling practice now in use involves an eccentric stabilizer welded to the drilling motor body near the lower end. For directional drilling, the drill string is oriented by conventional processes and drilling proceeds. To drill straight hole, the drill string, eccentric stabilizer and all, is rotated. This system strains the downhole assembly and is usually employed only above poly-crystalline diamond bits that do not demand geometric symmetry with the axis of rotation.
U.S Pat. No. 2,345,766 issued Apr. 4, 1944 and 2,375,313 issued May 8, 1945, by the same inventor, discloses apparatus responsive to drilling fluid flow to deflect the centerline of a pilot bit before the drill string rotation takes place. The drill string is lowered to place the deflected pilot drill head, which is moved laterally by drilling fluid flow, against the borehole wall. Drill string rotation then drills ahead and the drill string and full gage bit follows through the newly deflected hole. These were rotary drilling devices and were not known to be used, or usable, on drilling motors.
Russian publication 969,881 of 10/30/1982, in Drilling Technology discloses apparatus usable on drilling motors to skew the axis of rotation of the drill head driving output shaft relative to the motor body. The actuator that forces the axis to be skewed is responsive to drilling fluid flow but responds every time drilling fluid is caused to flow. No drilling can be done with the output shaft axis straight relative to the motor. The actuator force means and the gimbal that allows the force to skew the axis of the output shaft are quite similar in iunction to those aspects of the present invention. There are some differences in structure. The present invention distinguishes over the cited Russian system by the use of a remote control selector valve to control the skewing action. A skewed axis is the same as a deflected axis if the machine element deflected rotates on the deflected axis. The present invention permits the output shaft to, selectively, remain straight relative to the motor body while drilling fluid flows. The Russian apparatus can have a straight overall centerline only when the drilling motor is idle, primarily to ease transport of the down hole assembly along the well bore during round-tripping the drill string.
Efforts to allow down hole drilling assemblies, with and without down hole motors, to be used selectively for directional work and straight hole drilling has persisted for many years. No products are known to have evolved that permit drilling fluid flow controls to be used at the earth surface to select the drilling mode to be carried out down hole.
It is therefore an object of this invention to provide apparatus to change a down hole drilling assembly to select straight hole or directional drilling configuration by selectively actuating drilling fluid flow controls at the earth surface.
It is another object of this invention to provide an assembly to be attached, as an extension, to an existing down hole motor adapted to connect to the extension, to provide the motor with the ability to respond to drilling fluid flow controls, exercised at the earth surface, to either deflect the drilling axis or to hold it straight for drilling.
It is another object of this invention to provide a down hole drilling motor, adapted with an output shaft directional controling extension, with a proven remote control selector valve, situated in the extension, to respond to exercises of drilling fluid flow controls at the earth surface to deflect the output shaft from normal drilling to directional drilling.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached drawings and appended claims.